Sustainable Cross-linked Polymers with Potential for Recyclability

Abstract

Polymers are long chain molecules made up of repeat units called monomers linked end-to-end into giant molecules. A subset of these materials are cross-linked polymers, wherein the individual polymer chains are linked together into one continuous network. Unlike thermoplastics, cross-linked polymers are able to adopt a permanent shape and are stable under high temperature and solvent/chemically intensive conditions. Consequently, they are extremely useful for a multitude of applications, such as tires, insulation, adhesives, coatings, and various other products. Unfortunately, these favorable properties also prevent cross-linked polymers from being reprocessed to another shape or recycled through traditional means. Much research has been performed on producing cross-linked polymers that are capable of controllable reprocessing. However, most polymeric materials are derived from fossil fuel feedstocks and by virtue of their hydrocarbon backbones, are incapable of environmental degradation on reasonable timescales. Thus, there is still much to be developed in order to generate these materials sustainably. The overarching theme of my research was to produce cross-linked polymers that are both sustainable and recyclable. The first section (Chapter 1) of this thesis is a Perspective on the future of sustainable, recyclable cross-linked polymers. This is followed by studies (Chapters 2-5) on potentially sustainable cross-linked polymers that are capable of dynamic cross-link exchange through urethane bond exchange. In the final section (Chapter 6), the production of chemically recyclable, sustainable cross-linked polyester elastomers is detailed.